Ultra-short wave amplifier



March 2,' 1943.

' A. VAN DER zlEL ET AL ULTRA-SHORT WAVE AMPLIFIER Filed June 14, 1940 To SOURCE 0F Y ULTRA-SHORT *5 w-"AVES l' 3 /5 L1 rg E '5' kr :lamamv .Q 2 7 [l-r I i o f f 3 Hin-l- -I'l ?\awu lNvEN-foR s ALDERT VANDER ZIEL fao-:fw

ATTORNEY Patented'Mar. 2, 1943 UNITED ysTA'ri-:s PATENT OFFICE -ULTRA SHORT WAVE AMPLIFIER Aldert van der Ziel and Maximiliaan Julius Otto Strutt, Eindhoven, Netherlands, assignors to i Radio Corporation of America, a corporation oi' Delaware Application June 14, 1940,1Serial No. 340,514 In the Netherlands December 2, 19319 aclaims (cina-111) l This invention relates to an amplifying circuit` for ultrashort waves. f

In amplifiers for wave-lengths below 10 metres the dilculty is met that the input damping of the amplifying tube is very high. The strong damping of the input oscillatory circuit thus involved results in only a very low voltage occurring between control grid and cathode so that the amplification is small. The present invention has vfor its purpose to obviate this drawback.

The invention is based on recognition of thefact that the'input. damping o f the amplifyingtubes is composed of various components, First of all the so-called "electronic damping occurs which is due to the fact that the transit time ofA the electrons isnot negligibly small relatively to the period of the oscillations to be ampiifled. Due to this, a phase displacement is produced between the potential ofthe control grid and the electronic current owlng through the apertures of the control grid said phase displacement bringing about a damping. A second damping component is produced due to the voltage drop in the cathode lead which behaves for ultrahigh frequencies as an inductance. A volta'ge occurs through this inductance which leads to the extent of about 90 relative to the control grid voltage,

and consequently brings about a current across the control grid cathode capacity which is in anti-'phase with the control grid voltage and consequently exerts .a damping action. Finally, the voltage drop 4in the screen grid conductor has an action reducing the damping, since a voltage occurs through the inductance of the screen grid conductor, which voltage lags to the extent vof about 90 withrespect to the control grid voltage,

and consequently brings about aV current across latory circuit with the capacity of the screen grid relatively to the other electrodes, the natural wave-length of the said oscillatory circuit being located above the region of the waves to be amplied.

According to 'the invention use is made of a push-pull circuit of two amplifying systems, each of which comprises at least a cathode, a control grid, a screen grid and an anode, the cathodes of the two systems being connected to one another by a shortest possible conductor so as to 4provide negligible impedance while each of the screen grids is connected to the associated cathodes by an inductance which is so proportioned that `the input-damping of the circuit is` zero or negative. f y

In a push-pull circuit only -a high frequency voltage drop occurs through the parts of the cathode conductors which are not common. By

making these parts as short as possible the damping occurring due to the voltage drop in the cathode conductors may, therefore, be made very small. `In this case practically only the electronic damping still plays a part, and this may be suppressed by means of an inductance in the screen grid conductor which is so small that it need'not the screen grid control grid capacity, which is in phase with the control grid voltage, and consequently exerts an action reducing the damping. In normal tubes the influence of the inductances of the supply conductors for the other electrodes is small.

By increasing the inductance of the screen grid conductor it would in principle be possible to make the last mentioned damping reducing action so great that the resulting input damping becomes zero, or even negative. In practice, however, this appears not'to be possible in a normal amplifying circuit because to this end so great an inductance would have to be included in the screen grid conductor that it is physically no longer realizable. In fact, a coil having the required great inductancelconstitutes an oscilgive rise to resonance effect. In order to obtain a shortest possible connection between the cathodes of the two amplifying systems, the latter are preferably combined in one bulb.

In the case `of very short waves (wave-length below 4 metres) the inductance in the screen grid conductor required-for compensating the input damping is slightly dependent upon the frequency, and this on the one hand because in this region the frequencies to be amplified are only slightly lower than the natural frequency of the reactance coil utilized, and, on the other hand, because the dynamic slope of the screen grid current increases with an increase of the The invention'oifers the additional. advantage that the compensation is rendered easier. ac-

cording as the slope of the amplifying systems increases, wh'ereas with the use of a single amplifying tube, so far as the compensation aimed at would still be possible for comparatively great.

wave-lengths, this compensation is rendered more diilicult with an increase of the mutual conductance. In fact, in normal cases the damping brought about by the voltage drop in the cathode conductor is highly increased with an increase of the slope, whereas the electronic dampaaianca ing only slightly increases. Consequently, in a.- single tube the input damping highly increases with an increase of the slope, whereas in a pushpull circuit according to the invention this increase is small. IOn the other hand, innormal cases the screen grid slope increases with an in crease of the slope but to a'less extent than the cathode slope. In the push-pull circuit according to the invention the inductances in the screen grid conductors may consequently be made smaller, according as the slope of the amplifying systemis higher, whereas when using a single tube the required inductance would increase with anr increase o i the slope. Y

The invention will be more clearly understood by reference to the accompanying drawing showing, by way of example, one embodiment thereof.-

The input voltage which may originate, for example, from a dipole antenna is supplied to te'rminalsv I and 2, and inductlvely transmitted to the oscillatory input circuit 3. 'I'.he ends of the oscillatory circuit 3 are connected in 'push-pull relation to the control grids 3'4" of a pushpull amplifylng'tube l.' This tube contains two amplifying systems, each of which is constituted by a cathode', a control grid, a screen grid, a suppressorgrid` being connected tothe cathode and an anode of each section. The anodes have connected between them an oscillatory output circuit 5 from which the amplified' voltage may be derived by terminals l and 1.

'I'he cathodes of the amplifying -sections are connected toone' another by a shortest possiblel conductor. `Each of the screen grids is separate--V ly led out of th tube, and connected for high frequency to the catho'des by reactance coils 8 and 9. These coils are so proportioned that the input damping of the tube 4 is Azero or negative,

` so that the circuit 3 is notdamped by the tube,

or the dampirgis even reduced. The'required inductance value of the coils 8 and l is of the order of 10'l henry.

What is claimed is: 1

1. An amplifying circuit for ultra-short waves comprising a single-tube provided with two'sets of electrodes, each set including at least a single terminal cathode, a control grid, a screen grid and an anode, the cathode terminals of the two electrode sets being connected toone another inside the tube by a shortest possible conductor and connected to a single lead only extending to the exterior of the tube and the screen grids each having a separate connection to an external terminal of the tube, and a high frequency path lncluding an inductance coil between each of the external screen grid terminals and the single lead connected to the cathodes, said inductance coils being so proportioned that the input damping oi' the circuit is substantially negligible.

2. In combination, an evacuated envelope containing a pair of similar electrode systems each comprising a single terminal cathode, -a control grid, a screen grid and an anode, the cathodes being internally connected at their terminals by a path having so little inductance that very little input damping is produced thereby, said internal cathode connection being connected to a single' lead oniy.extending to the exterior of the tube and the screens being brought out separately whereby interchangeable amounts of inductance '-may be connected between screens, said latter inductance, by virtue of said small inter-cathode inductance, being effective to eliminate input damping without being so large as to resonate with the screen capacities at any frequency near the operating frequency.

' 3. In combination with a pair of electron discharge paths contained in a single envelope, each to the transit time of the electrons between each cathode and signal grid being comparable to the frequency of the oscillations to be amplined, and

Y means for minimizing said damping eiect on the input circuit comprising an inductance connected between eachyscreen grid terminal and the single lead connected `to the cathodes.

ALBERT vm naa ZIEL. 4

JULIUSOTIO STRUTT.' 

